Drilling fluids



Patented Feb. 20, 1 951 DRILLING FLUIDS Paul W. Fischer, Long Beach, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California No Drawing. Application July 22, 1948, Serial No. 40,171

Claims.

This invention relates to drilling fluids emplayed in the drilling of oil and gas wells, and to a particularly successful procedure for preparing such drilling fluids. This invention more particularly relates to drilling fluids of the type generally referred to as the nonaqueous or oil-base class of drilling aids.

In drilling an oil or gas well by means of rotary drilling tools, a hollow drill pipe known as a drill stem having a bit attached to the lower end is extended downwardly through the well bore and rotated while the bit is pressed against the working face in the formation at the bottom of the hole. The action of the rotating bit grinds away the formation as the drilling progresses. A fluid, commonly termed a drilling mud, is circulated downwardly through the drill stem, through the bit against the working face of the hole and then upwardly toward the surface through the annular space between the drill stem and the wall of the borehole. This drilling fluid serves a number of purposes among which are cooling and lubricating the drill bit, suspending and removing cuttings irom the borehole, sealing the borehole wall to prevent loss of drilling fluid into the surrounding formation, preventing the flow of fluids from the formation into the borehole by applying a hydrostatic pressure to the formation, and fulfilling other requirements.

The nature of drilling fluids commonly used in boring oil or gas wells divides them roughly into two classes: the water-base and the oil-base drilling fluids. The present invention is directed primarily toward an improved oil-base drilling fluid which is prepared from a major proportion of -mineral oil and a minor proportion of water and addition agents.

Oil-base drilling fluids have been previously proposed which contain considerable quantities of asphalt and similar solid hydrocarbon-like materials for the purpose of sealing the walls of the borehole. The preparation of oil-base drilling fluids containing such normally solid constituents requires heating of the asphalt or other solid" material and renders preparation of these fluids somewhat difflcult in the field at the site of the well. Handling of molten asphalt at the well site presents a serious disadvantage which is completely eliminated through the use of the improved drilling fluids disclosed herein. Some oilbase fluids are prepared from finely ground asphalt. Such powdered asphalt is not easily handied and may not be completely incorporated in the drilling fluid.

Oil-base drilling fluids have been previously proposed which contain certain metal soaps which are employed as emulsifying agents in order to stabilize th suspension of solid matter employed in the drilling fluid or to increase the stability of an emulsion of oil and water. The soaps often employed are those of the fatty acids including acids which are dioleflnic or trioleflnic invention which is considerably less than the filtration rates obtained in other drilling fluids in which oil-dispersible soaps containing doubly or triply unsaturated anions are employed. With the drilling mud of this invention it is apparent that th degree of unsaturation of the anion of the soap is relatively unimportant in comparison to the effect of using a combination of an oildispersible and a water-dispersible metal soap according to this invention. The water-dispersi- 'ble soap materially assists the dispersion of the oil-dispersible soap to form a drilling fluid according to this invention having a high emulsion stability and a filtration rate which is zero in most cases.

It is a primary object of this invention to provide an improved drilling fluid of the oil-base type which permits increased drilling rates over the conventional oil-base or water-base drilling Another object of this invention is to provide an oil-base drilling fluid which comprises an unusually stable emulsion which is highly efiicient in suspending drilling cuttings while having a filtration rate of substantially zero and being easily circulated through the hole.

Another object of this invention is to provide an improved method of drilling oil or gas wells by employing an emulsion-bas drillin fluid as described herein.

An additional object of this invention is to provide an improved method for preparing oilbase drilling fluids in which a highly stable type of oil-external emulsion is apparently formed from a light oil and a heavy oil employed together with an emulsiflcation agent and a small quantity of water and a hydratable clay in the presence of an excess of a basically reacting material.

Another object of this invention is to provide an oil-base drilling fluid which is characterized by being capable of resisting the adverse effects of up to about 20% to 30% water cutting without suffering undue settling of the weighting material or loss of other desirable physical properties.

A further object of this invention is to provide an improved drill ng fluid containing a major proportion of crude oil and having a filtration rate of substantially zero and a funnel viscosity (1500/qt.) of between about and 359 seconds.

It is another object of this invention to provide a crude oil base drilling fluid containing water and a small amount of rosin acid soaps by means In particular the oil-dispersible soap disclosed in the present invention gives a filtration rate to the drilling fluids or" this 3 of which oil and gas wells of increased productivity may be drilled without adversely affecting the producing formations.

It is a further object of this invention to provide a method of reclaiming used oil-base drilling fluids for reuse. v

Other objects and advantages of this invention will become apparent tothose skilled in the art as the description thereof proceeds.

Briefly, the present invention comprises an improved drilling fluid prepared from a special emulsion as the suspending medium. This suspending medium is preferably produced by compounding mineral oil together with emulsifying agents and water according to a special procedure as hereinafter more fully described. The emulsifying agent comprises metal organic acid soaps, including a water-dispersible and an oil-dispersible soap. These soaps may be added as'such but are preferably formed by metathesis of the water-dispersible soap with a suitable basically reacting inorganic metal salt to form the oildispersible soap.

In one modification of the drilling fluid, the oil phase of the emulsion comprises a light oil such as a distillate together with a heavy oil which contains unsaturated or aromatic constituents or both. Cracked fuel oil in particular as well as certain types of lubricating oil extracts are well suited as heavy oils to the preparation of the improved drilling fluid.

In another modification of this invention the oil phase comprises crude oil such as stabilized crude as is readily available in all oil fields or topped crude available in refineries. The heavier types of crude petroleums have been found to be preferable such as those containing a relatively large residual fraction. Residual fraction is meant to include those hydrocarbon materials boiling above about 700" F. Crude petroleums containing substantial quantities of such a residual fraction and also containing considerable hydrocarbon compounds of sulfur such as the crude produced from the Santa Maria Valley (California) have been found Well adapted to compounding the drilling fluid contemplated by this invention. The use of a mixture of light and heavy oils in the formulation of drilling fluids is described and claimed in the copending application of Paul W. Fischer and Frederick S. Scott, Serial No. 4,213, filed January 24, 1948.

In the preferred modification of this invention, a minor but effective proportion of a hydratable clay such as Wyoming bentonite together with water is added to the mixture to improve the gel strength and thixotropic properties. This suspending medium prepared as hereinafter more fully described may contain weighting agents added specifically for increasing the specific gravity of the drilling fluid, if such materials are desirable in the drilling of a given well.

In addition, the present invention particularly relates to successful procedures for compounding the drilling fluids of this invention in which the emulsion is first formed from the light oil, emulsifying agent and water and is subsequently extended with the heavy oil and to a simplified method readily adaptable to field practice in which selectedcrude petroleums are employed.

A successful drilling fluid must have certain physical properties in order for it to perform satisfactorily and fulfill the requirements needed in oil or gas well drilling. Certain of these requirements have been given above and the physical properties involved in fulfilling these include a low filtration rate and a satisfactory viscosity. The filtration rate determines the ability of the drilling fluid to seal the wall of the borehole against the loss of fluid into the formation and the passage of fluids from the formation into the well. The viscosity gives a measure of the ease with which the drilling fluid may be handled and pumped through the hole. The thixotropic properties as for example, the gel strength, determine the ability of the drilling fluid to suspend and remove from the hole material broken out of the formation by the action of the drill bit and retain cuttings in suspension should the fluid circulation be stopped. The dr lling fluid further must readily release these materials from suspension when the fluid is agitated at the surface prior to reintroduction into the hole. The improved oil-base drilling fluid of this invention fulfills the requirements recited above and after thorough field testing has I been found to form a highly desirable and successful drilling fluid.

The ability of the drilling fluid to effectively seal the wall of the borehole may be determined by means of a simple filtration test in which the drilling fluid is pressed under pressure against a permeable membrane or filter. The quantity of filtrate obtained under certain standard conditions of pressure and temperature is a measure of the wall sealing ability of the mud, a property which is also termed the cake forming, filter loss,

sealing, or filtration characteristics. Such a standardized procedure for determination of the I filtration rate is prescribed in Recommended Practice on Field Procedure for Testing Drilling Fluids, A. P. I. code No. 29, second edition, published July 1942.

A measure of the ease with which the drilling fluid may be circulated through the hole during. drilling is indicated by the viscosity. A viscosity determination may be made by following a standardized procedure given in Recommended Practice on Field Procedure for Testing Drilling Fluids A. P. I. code No. 29, second edition, published July 1942. The property thus obtained is known as the Marsh viscosity or the funnel vis v cosity and is given by the time in seconds reing procedures to have a filtration rate which is not only substantially less than that of the conventional drilling fluids normally employed in the well drilling, but which is in most cases substantially zero. This drilling fluid is free from fermentation problems as well as being com- 1 pletely inert to the detrimental action of salts I and material cut from the formation during the drilling of the well bore. Actually it has been found that the quality of the fluid improves with use. This may be due to the presence of materials cut from the formation or the combination of ingredientsused in formulating the drilling fluid, although these facts have not been estab-.-

lished. .It has been noted that the gel strength of the fluid increases with drilling and consequently the characteristics of a drilling fluid are often better when the second or third wells are drilled than in the first one. This improvement of the fluid with use appears to be characteristic of the drilling fluids according to this invention. This improved drilling fluid may be repeatedly used in the drilling of a number of different wells by virtue of its inertness to materials encountered in the formation during drilling and may be used in drilling caving formations.

As briefly described above, the drilling fluid of the present invention may contain a major proportion of two different mineral oils in an emulsion formed with an aqueous suspension of a hydratable clay. It also contains an emulsifying agent comprising two metal soaps which may be formed by the reaction of a metathesizable water-dispersible metal organic acid soapand an excess amount of a basically reacting compound. The oil required may comprise a stabilized (substantially gas free) crude petroleum available in every oil field or it may comprise a topped crude (gas and gasoline free) available from oil refineries. When drilling a known field, crude oil available from production of the other wells may be adapted for compounding this drilling fluid. Preferably, the crude petroleum has a gravity of between about and A. P. I. or higher, although good drilling fluids have been prepared from crudes having gravities as low as 10 A. P. I. such as from Santa Maria Valley (California) crude. It is desirable to select crudes containing a substantial proportion of polymeric constituents of high molecular weight in considerable proportion such as those having from about to as high as about 85% by volume of a residual fraction which is nonvolatile below about 700 F. A suitable oil may be prepared from a light crude petroleum which is relatively deficient in a residual fraction by blending it with cracked or straight-run residuum to supply the desirable polymeric high molecular weight constituents or by incorporating a proportion of heavy crude to bring the proportion of residual compound up to the desired value. Those crudes having too high amounts of residual fractions may be blended with a cutter stock such as a gas oil or a light crude. Crude petroleums having as high as 5% by weight of sulfur in the form of hydrocarbon-sulfur compounds such as those petroleums found in California are desirable, particularly the crude produced in the Santa Maria Valley such as Santa Maria and Orcutt crudes. Preferred crudes have a gravity of about 25 A. P. 1., a viscosity at 100 F. of from about to 1000 seconds (Saybolt Universal), and between about 20% and of a gas oil fraction.

The oil employed in compounding the improved drilling fluids of this invention may also comprise a combination of a light mineral oil with a heavy mineral oil. The light oil used is preferably one boiling between about 300 F. and 760 F. such as gas oil, kerosene, Diesel fuel, and the like. The heavy oil used is normally liquid having a gravity of between about 10.0 and 250 A. P. 1., the major proportion of which boils above about 760 F. These heavy oils desirably contain a substantial proportion of high molecular weight normally liquid unsaturated constituents includin olefinic and/or aromatic molecules such as are present in cracked residuums, cracked fuel oils, petroleum extracts, and the like, having viscosities in the range of from 26 to 100 S. S. F. at 122 F. Heavy oils containing substantial quantities of sulfur have been found applicable.

,6. minor proportion of a hydratable clay such as Wyoming bentonite may be incorporated into the drilling fluids of this invention to serve the purpose of improving the stability of the emulsion and the suspension of weighting agents which may be added, if required. Since the quantity of hydratable clay thus incorporated is very minor, between less than 0.1 to about 5.0% by weight, it does not serve the purpose of a weighting agent since the addition of the hydratable clay results in an immeasurably low increase in the specific gravity of the drilling fluid. A substantial increase in the stability of the emulsion, is however, effected.

A highly important ingredient in the improved drilling fluid preparation is the agent employed to impart emulsion stability, and desirable wall sealing properties to the fluid. This agent comprises the combination of a water-dispersible and an oil-dispersible soap of a saturated or unsaturated cyclic organic acid. The most desirable soaps are prepared from the unsaturated cyclic acids such as the rosin acids or tall oil acids. Saturated cyclic acids such as naphthenic acids may be employed if the preferred rosin acids are not available. The preferred soaps may be made through direct neutralization of natural resins, gums, or other materials containing subsbtantial quantities of cyclic unsaturated acids such as abietic acid and abietic anhydride.

It has been found that by carefully selecting or preparing the rosin acid soap, particularly superior drilling fluids are obtained according to this invention. Certain of these rosin acid soaps are both waterand oil-dispersible when they are prepared in a controlled manner. For example, these desirable rosin-acid soaps may be prepared from either wood or gum rosin by a method which includes the steps of decarboxylation of the rosin to form a decarboxylated material having a certain acid number, saponifying this material with caustic under pressure to form the soaps, and dehydration of the resulting soap to a fairly low water content such as about 10% or lower. Using caustic potash in the saponification, a potassium soap may be prepared which is both waterand oil-dispersible and which contains about 40% unsaponified organic material such as abietic acid, pinene, terpenes, terpeneol, sterols, rosin alcohols, and the like, about 50% potassium or other alkali metal abietates and like soaps, and about 10% water. Other ingredients in minor proportion such as viscosity depressants.

may be added to reduce the product viscosity, if

desired.

The particular rosin acid soap prepared as above described and having the dispersion properties given is a very desirable one in the preparation of drilling fluids according to the methods outlined herein. Such soaps are therefore the preferred form of rosin soaps since they are both waterand oildispersible and readily metathesized to other oil-dispersible soaps such as those of the alkaline earth metals.

It is preferred that the water-dispersible soaps of these acids be employed such as the ammonium or alkali metal soaps, since these may be readily metathesized by the action of basically reacting divalent or polyvalent metal compounds to cause at least a partial conversion to oil-dispersible and water-indispersible soaps of these acids. The oxides or the hydroxides of the alkaline earth metals may be thus employed. Basically reacting compounds of other metals such as lead, iron, aluminum, manganese, and the like, may also be applicable to form oil-dispersible soaps. The

quantity employed is preferably less than. two. equivalents of salt per equivalent of water-edispersible soap to be metathesized. The emulsifying agent preferred in these drilling fluids comprises a mixture of a sodium water-dispersible soap and a calcium oil-dispersible soap of rosin acids so prepared.

During the preparation of the improved drilling fluid, at least a portion of the water-dispersible soap specified above is desirably converted by metathesi into an oil-dispersible soap to form an emulsifying agent comprising a mixture ofv the two types of soap, A drilling fluid is thus formed which comprises an emulsion of the aforementioned oils, a minor amount of water and has the desired degree of stability and the required physical properties. It is believed that by this procedure, involving the use of a combination of waterand oil-dispersible soaps in the method of preparation hereinafter more fully described, a type of emulsion is formed which is unusually stable. 7

A procedure which is well adapted to mixing homogeneous drilling fluids from crude petrolewms according to this invention and which is exceedingly simple to perform in the field has been found. In this method, a volume of crude oil corresponding to about of the total quantity'of crude to be used is taken. The waterdispersible soap, water, basically reacting agent, and clay, if any, are thoroughly mixed to form a concentrate with this volume of crude oil. The concentrate is then blended with the remaining quantity of crude oil to form the final mixture. This preparation is best performed in tanks suitably connected and provided with pumps that the contents may be circulated. The soap, clay, water, and other ingredients may be added in two batches if desired by taking about a 5% volume of the fluid, mixing in additional quantities of ingredients to form more concentrate, and recirculating the second concentrate with the drilling fluid. In general, the drilling fluids thus prepared may contain from about 60% to as high as about 99% by weight of crude oil depending upon the lphysical properties desired.

In order to obtain a satisfactory emulsion for. use as a drilling fluid from the materials described above, particularly when the oils used comprise a selected light oil and. a heavy oil in accordance with the invention described in the aforesaid application Serial No. 4,213, flled January 24, 1948,

a specialized procedure of mixing and compounding should preferably be followed. In the preferred modification for preparing the drilling fluids of this invention, the following order of mixing is employed:

Step 1 The total amount of light 011 is added a a .All of the metathesizable water-dispersible soap is added to the suspension and mixed thoroughly.

I Step 3 The hydratable clay is next added as a dry powder or as an aqueous suspension to the above mixture and thoroughly agitated to form an emulsion.

Step 4 To this emulsion the heavy oil is slowly added and thoroughly agitated until a homogeneous system is achieved.

'By following the procedures given above the basically reacting salt interacts with and metathesizes the Water-dispersible soap in the presence of water added subsequently to form an emulsi- .fying agent comprising a mixture of water-dispersible and oil-dispersible soaps. This agenteffects the thorough emulsification of the clay or clay-water suspension with the oils used to form the drilling fluid. When the clay is added as a dry powder an emulsion containing a minimum amount of water may be formed from less than 1.0% of water present in the soaps and other ing'redients.

and other ingredients forms an emulsion containing less than about 1.0% by weight of water. In the preferred modification, the water-dispersible component of the emulsifying agent is sodium rosin acid soap and the basically reacting salt employed is calcium hydroxide or commer- The oil-dispersible matecial hydrated lime. rials resulting from the metathesis are calcium rosin acid soaps and the combination of the two types of soap is believed to be responsible for the formation of an emulsified oil-base drilling fluid which has proved unusually satisfactory both in laboratory testing and actual field practice and superior to other oil-base drillin fluids in which merely one emulsifying agent is used.

The drilling fluids of this invention may also soap may also, if desired, be premixed with the oil prior to entering the hole. During this circulation, the other ingredients such as water, clay,

basically reacting compounds for metathesis.

weighting agents, etc. may be incorporated.

The addition of certain ingredients which increase the fluid gel strength may be made in the form of alkali metal or ammonium silicates, carbonates, or chromates as aqueous solutions. Commercial water glass as a 40% aqueous solu-' tion of sodium silicate is particularly satisfactory. The use of these gel strength improvement agents is more clearly set forth and claimed in copending application Serial No. 10,559, filed February 1 24, 1948. The drilling fluid described in conjunction with Example XIII incorporates 1% of such an agent.

Typical specifications of the improved drilling fluid of this invention are given below:

The weight of the drilling fluid "prepared as above described has a minimum value of about pounds per cubic foot which gives suflicient In these cases no water may be added as such and the water present in the soaps, oilf 1 However, where additional weight is required, the fluid weight may be readily increased by incorporating a finely divided weighting agent such as 1 calcium carbonate, barium sulfate, iron oxide,

and the like. The weight may thus be increased to as hi h as 120 pounds per cubic foot if needed.

The drilling fluid viscosity may vary widely depending upon drilling temperatures and the composition. Generally, it is desirable to maintain the funnel viscosity 1500/ qt.) at a value between 100 and 350 seconds measured at the temperature it comes from the well. A typical viscosity is in the range of from 200 to about 260 seconds and temperatures of the fluid leaving the well and entering the settling pits vary between about 80 F. and about 130 F. depending on depth.

Should the viscosity rise during drilling with the crude oil base fluid, it is more easily decreased by addition of a light oil such as Diesel fuel, gas oil, or a light crude. To raise the viscosity, further quantities of crude or residuum may be added.

These drilling fluids employing crude oils have been found to resist the efiects of water picked up during drilling. Desirable properties remain even though as much as 20% to 30% of Water is present as a water-in-oil emulsion. This propcity of the drilling fluid characterizes it as a highly desirable type to employ.

The quantity of light oil may be varied from as low as less than 1% by weight to as high as about 25% by weight de ending upon the physical properties desired in the drilling fluid ultimately pro- :duced and the temperature at which the drilling fluid is employed. It is preferable, however, to "employ from about 10% to about 15% by weight of light oil for wells of about 4000 to 6000 feet in and possess a viscosity in the range of from 20 to 40 S. S. F. at 122 F. When crude oil is used, between 60% and 99% by volume is employed. The quantity of hydratable clay incorporated in the drilling fluids of this invention is preferably about 0.5% by weight although a range of from as low as 0.05% to as high as 5% by weight or higher permits the formulation of satisfactory fluids. Between about 0.05% and by weight of water is employed which may be added as such or present in the various ingredients. Especially good fluids are obtained with about 0.7% water.

The quantity of water-dispersible alkali-metal soap is preferably around 5% by weight. However, quantities as low as about 0.1% by weight or less to as high as about 10% by weight may be used. The quantity of lime or other source of basically reacting compound to form the oil-dispersible soap by metathesis of the water-dispersibIe alkali-metal soap is sufficient to permit a partially complete or substantially complete metathesis. A mixture of oil-dispersible and waterdispersible soaps as the emulsifying agent results. It is. indicated that the presence of the waterdispersible soap materially assist in dispersing the oil dispersible soap in the system. When about 5% by weight of alkali-metal soap is employed, 1.0% to 1.5% by weight of hydrated lime has been proved satisfactory.

The quantities of individual constituents involved in the preparation of a typical drilling fluid, according to this invention, may be obtained by reference to the following example:

Example I In connection with the drilling of an experimental oil well with the drilling fluid of the present invention, a total of 390 barrels of this fluid was prepared by preparing a number of -barrel batches of the drilling fluid employing the quantities given below:

. Weight Weight Ingredient Pounds Per Cent Diesel Fuel, Domestic 2, 210 13. 2 Lime, Hydrated 168 1. 0 Sodium Rosin Soap"- 670 4. 0 Fuel Oil, Light Domesti 12,800 76. 8 Water. 788 4. 7 Wyoming Bentonite, Dry 0. 3

Total .Q. 16, 686 100. 0

Physical characteristics of the domestic Diesel oil employed as the light oil in formulating the drilling mud given above is given below:

Inspection of the light domestic fuel oil employed as the heavy oil in the formulation of the improved drilling fluid gave the following:

Gravity, A. P. I 14.5

Flash point, "F 170 Viscosity, SSE at 122 F., seconds 36 Ash, per cent by weight 0.06 Sulfur 2.5 BS&W cent, per cent by volume 0.1

Properties of the drillin fluid employed in the experimental oil well were as follows:

Mud weight, pounds per cu. ft to 61 Viscosity at F., 1500/1000 Fluid loss per hour, ml N11 Water, per cent by weight 5.3 to 5.8

This drilling fluid was employed in completing an oil well drilled in the Dominiguez Field of Southern California. The well had been drilled to a depth of about 3900 feet employing a conventional water-base drilling mud at which depth casing was set and cemented. The oil-base drilling fluid of this invention was substituted for completing the hole through the producing formation to a depth of about 4600 feet. During the drilling, the mud weight, fluid loss, mud cake, and gel strength remained constant at satisfactory values. The viscosity of the fluid varied somewhat due to the change in temperature of the fluid depending upon the length of time the fluid was subjected to shearing action in the hole. Upon prolonged drilling the fluid temperature did not increase above 118 F. at the discharge line. Gas cutting was evidenced but the gas broke immediately from the fluid in the pits and caused no difliculty- A comparison of the drilling rates obtained in certain formations using the drilling mud of this invention and water-base 11 Tdrilling fluids showed that the drilling fluid'of this invention may be expected to permit a drilling rate as high as about 20% above that permitted with water-base fluids. These comparisons were made from data obtained from other '1 "wells drilled into the same producing formations fin the immediate vicinity of this experimental i well.

" The oil-base drilling fluid was removed from *the hole, the well was flushed with crude oil and placed in production. The production rate of 'the experimental oil well thus completed compared very favorably with wells in the vicinity .cornnleted into the same producing zone.

Effectiveness of various soaps in the oil-basedrill ng fiuid of t e present nvent on as reviously described has been evaluated by laborav 2 tory experiments.

Example}! .in minutes, zero ml. in one-half hour and a ;Marsh viscosity 500/500 at 80F. of 160 seconds. The drilling fluid thus prepared corresponds to the preferred modification invention.

Example III 'It may be shown that drilling fluids having the same desirable properties may be prepared ac- :cording to the preferred method given previously with the exce tion that the oil-d spersible soap "formed by metathesis in the preferred modification is prepared separately and incorporated in "the drilling flu d together with a water-dispersible soap. A drilling fluid was prepared from a gas oil to wh ch was added 2.0% by weight sodium rosin acid soap, 2.0% by weight calcium rosin acid soap, the latter having been separately prepared, 0.5% by weight of hydratable clay, and 4.5% by weight of water. By following the preferred procedure, but without adding the light domestic fuel oilor heavy oil the product appeared as a two-phase emulsion, the quantity of on external emulsion being the greater. Upon addition of the light domestic fuel oil which amounted to about 75% by volume of the finished flu d, a reasonably uniform system resulted. The drilling fluid thus prepared exhibited a filter loss :of zero ml. in 15 minutes, zero ml. in one-half hour and had a March viscosity 500/500 at 80 F. l'of 180 seconds. Comparison of'the drilling fluid thus prepared with the drilling fluid in Example II shows that the presence of sodium hydroxide formed during the metathesis has a desirable effect since a one-phase emulsion-was formed in Example II.

Example IV The presence of the oil-dispersible calcium :rosin acid soap is believed to be of primary importance in forming stable emulsions in drilling fluids of the present invention and imparting thereto filter loss rates which are substantially zero. A drilling fluid according to this invention was prepared in which 4.0% by weight of calcium of drilling fluid of this product resulted which gave a fluid loss of zero ml.

rosin acid soap was dispersed in the gas oil (light oil) according to the method previously described together with 0.5% of hydratable clay and 4.5% by weight of water. The calcium rosin acid soaps are less readily dispersed in the absenceof the sodium rosin acid soap. In the absence of the heavy oil (light domestic cracked fuel oil) a uniform oil-external emulsion resulted and after-in:

corporation of the heavy oil a homogeneous drilling fluid resulted.

Analysis of this fluid indicated a filter loss of 'zero ml. in 15 minutes, zero ml. in one-half hour and a Marsh viscosity 500/500v at F. of 235 seconds.

The mixture wasa completely satisfactory drilling fluid as far as physical properties are concerned and indicated the desirability of employing the sodium rosin acid soaps in conjunction with calcium rosin acid soaps toaid dispersion of the calcium soaps in the oil.

Example V The use of the sodium rosin acid soaps alone according to the method of this invention did not result in a drilling fluid having the same low filter loss or the same degree of stability as those prepared using a water-dispersible and an oildispersible soap, as previously described in Ex 'amples I to IV, inclusive. Incorporation of 4.0%

of sodium rosin acid soap in gas oil (light oil) with 4.5% water and 0.5% hydratable clay according to the preferred method gave a very thick emulsion which was predominantly water external. Subsequent incorporation of the heavy oil gave a uniform drilling fluid which had "a The use of oil-dispersible rosin acid soaps prepared from other materials than rosin but which contain substantial quantities of rosin constituents such as abietic acid and abietic anhydride permits theformation of satisfactory drilling fluids. One of these materials is tall oil produced as a by-product in wood pulping. The

.incorporation of 4.0% by weight of an oil-dispersible calcium tall oil soap in gas oil with 0.5% clay and 4.5% water resulted in the formation of a uniform oil-external emulsion prior to the addition of the heavy oil. After adding the heavy oil a, homogeneous system resulted and the drilling fluid thus produced exhibited a filter loss of zero ml. in 15 minutes, zero ml. in one-half hour and a Marsh viscosity 500/500 at 80 F of seconds. v I

The use of organic acids having different dc.- grees of unsaturation to form the oilor waterdispersible soaps in the drilling mud of the pres ent invention is indicated in the following examples: i Example VII A drilling fluid was prepared according to the preferred procedures given above from gas oil, a water suspension of clay and 4.0% by weight of calcium oleate. A uniform oil-external emulsion was thereby formed and following the addition of the light domestic fuel oil-which comprises the major portion of the drillingmud-a uniform system was achieved. The filtration 13 rate, however, of such a drilling fluid was not as desirable as in the drilling muds containing the preferred emulsifying agents described above. The filtration rate was found to be 1.5 ml. in 15 minutes, 2.0 ml. in one-half hour and a Marsh "viscosity 500/500 at 80 F. was 190 seconds.

Example VIII The presence of excess base in a calcium oleate drilling fluid prepared in the same manner as that prepared in Example VII caused an increase in filtration rate and a decrease in viscosity. The mud thus prepared contained 4.0%

by weight of calcium oleate to which had been added a 93% by weight excess of lime based on the quantity of oleic acid. N With 4.5% water, 0.5% clay a stable oil external emulsion resulted which gelled upon standing. A uniform final "product was obtained upon addition of the heavy oil. The filtration rate was 4.5 ml. in 15 minutes,

6.5 ml. in one-half hour and had a Marsh viscosity 500/500 at 80 F. of 160 seconds. The use of excess base in the presence of an insoluble soap of a singly unsaturated acid is thus shown to form drilling fluids which are relatively un- Qdesirable compared to the preferred drilling fluids specified above.

Example IX The calcium soaps of linseed oil acids were prepared. The linseed oil employed contained about 28% by weight of dioleflnic acids and about 60% by weight of triolefinic acids. mixing 4.0% by weight of these calcium linseed Upon soaps with a suspension containing 0.5% clay and 4.5% water in gas oil a two-phase emulsion resulted which was predominantly oil external.

'-A uniform fluid was obtained after incorporating different from the drilling fluid prepared according to Example VII, and indicates that the degree of unsaturation of the anionic constituent of the soap has virtually no effect on the physical properties of oil-base drilling fluids prepared according to this invention.

Drilling fluids prepared from mixed acid soaps are shown to be definitely inferior to drilling fluids prepared according to this invention by the following examples:

Example X A drilling fluid containing 2.0% by weight calcium rosin acid soap together with 2.0% by weight of potassium oleate was prepared according to the method given above. A mixture of water-external and oil-external emulsions resulted and the final fluid formed after addition of the heavy oil indicated some separation of phases. The filtration rate was found to be 3.5 in minutes, 4.1 ml. in one-half hour, and the fluid had a Marsh viscosity of 150 seconds.

Example XI A drilling fluid prepared according to the preferred method of this invention. but which contained 2.0% by weight of calcium rosin acid soap andt2'.0% by weight of sodium naphthenatealso formed two separate emulsions in gas oil. Following incorporation of the heavy oil a fluid resulted which tended to separate upon standing. The filtration rate was found to be 1.0 ml. in 15 minutes, 2.0 ml. in one-half hour, and the fluid had a viscosity of seconds.

Comparison of Examples X and XI indicates that although the drilling fluids thus prepared did not have as desirable physical properties as did the preferred drilling fluids described in Examples I to IV, inclusive, the presence of waterdispersible naphthenate soaps is preferable to the presence of water-dispersible oleate soaps.

Example XII A drilling fluid was prepared from gas oil, 5.0% by weight hydratable clay-water suspension, and 4.0% of a calcium naphthenate soap. A twophase predominantly oil-external emulsion resulted and after mixing in the heavy oil a uniform fluid was formed. The filtration rate of this fluid was found to be 2.0 ml. in 15 minutes, 2.5 ml. in onehalf hour and the fluid had a Marsh viscosity at seconds. Naphthenic acid soaps are shown to be superior to the oleflnic and unsaturated acid soaps.

The above examples are intended to show the desirability of using a water-dispersible rosin acid soap and an oil-dispersible rosin acid soap in conjunction with a light oil and a cracked or aromatic heavy oil in the preparation of desirable oil-base drilling fluids. The substitution of mono-olefinic, diolefinic or trioleflnic fatty acid soaps for the preferred rosin acid soaps has thus been indicated as less desirable. The effect of excess base is shown in Example VIII to have undesirable eflects on drilling fluids containing calcium oleate soaps; whereas, desirable efiects are noted when excess quantities of base are employed with the preferred drilling fluids of the present invention, such excesses of base arising during the metathesis reaction.

The following examples are illustrative of the preparation and use of crude oil-base drilling fluids in the completion of wells into the producing formation. Primarily these drilling fluids are completion fluids, although they may be employed in drilling the total depth of the well.

Example XIII In the Santa Paula oil field of Southern California an oil well had been drilled to a total depth of 2131 feet with a conventional waterbase drilling fluid. At this depth a crude oilbase drilling fluid, according to this invention, was prepared for completion of the well through the producing formation to a total depth of 3316 feet. The crude oil employed in the preparation of this batch of drilling fluid a 50-50 mixture of two types of crude oil, one having a gravity of 285 A. P. I. and the other a gravity of about 16.9" A. P. I. These crude oils had the following physical characteristics:

Heavy Loss, Volume Per Cent feet.

The gasoline fraction of the above analyses had a 410 F. end point and the gas oil fraction had a 4-1 second viscosity. A -barrel volume of the light crude was placed in a barrel tank fitted with a circulating pump and a mixing gun so that the contents of the tank could be thoroughly circulated. A concentrate was prepared the light and heavy crude oils, the properties of which are given above.

Subsequently two .20- barrel volumes of the fluid obtained, as just described, were taken and the proportion of ingredients given above were subsequently added vto form two additional batches of the concentrate. These concentrates were then mixed to form approximately 450 barrels of drilling fluid.

The weight per cent of ingredients used in preparing the fluid is given below:

, Per cent Light crude 452 Heavy crude 46.2 Hydrated lime 0.5 Rosin soap 5.8 Water -2 1.3 ,Wyoming bentonite 0.8 .Unslacked lime 0.2

To the resulting fluid was then added 1% by weight of a 40% aqueous solution of commercial water glass to improve the gel strength properties of the drilling fluid. Finely powdered calcium carbonate and barium sulfate were mixed in with the drilling fluid to raise the weight thereof to about 80 pounds per cubic foot.

This drilling fluid was employed to drill through the main producing formation in the well referred to above froma depth of 2131 feet to 3316 At a depth of 3300 feet the water content was found to be 2.0%. During the drilling, samples taken of the fluid indicated that the fluid weight varied between 75 and 85 pounds per cubic foot, the viscosity varied between about 165 and about 235 seconds (1500/qt.), and the gel strength increased from about 3.5 to 6 pounds per100 square feet. At a depth of 2950 feet, the viscosity rose to a value of about 324 seconds at which point 80 barrels of Diesel oil were blended intothe. drilling fluid to reduce the viscosity.

The completed well came into production flowing at a rate of 200 barrels per dayand was the only one at the time flowing at such a rate in the Santa Paula area. The production rate gradually decreased to about 100 barrels per day. The comparison-of this well with adjacent wells indicate that the completion was exceedingly successful and that an unusually good well was obtained- This is attributed to the fact that the i drilling fluid performs very well'during drilling through producing horizons and that the permeable sand or other formation through which oil is obtained is not harmed or adversely affected by the drilling fluid as is apparentl the case with most other fluids. r

completion of 5255 feet.

7 .16 Example XIV The oil-base drilling fluids according to this invention were employed in redrilling an oil well in the Santa Maria Valley of Californa. Two separate batches of fluid were mixed to give a total volume of about 460 barrels. A 20-barrel volume of crude oil was used in preparing the concentrate which contained 350 pounds of hydrated lime, 3600 pounds of an 85% aqueous solution of potassium rosin acid soaps prepared as in Example XIII, one barrel of water and 400 pounds of Wyoming bentonite. The properties of the crude are as follows:

Gravity, A. P. I 24.9

Water (less than 1%) Viscosity at 100 F. SSU 187 Sulfur (per cent by weight) Distillation Inspection: Gasoline, volume per cent 26:1

Gas oil, volume per cent 28.6 Residuum, volume per cent 45.2 Loss, volume per cent 3.1

The concentrate was mixed for ten minutes and then circulated with 210 barrels of crude for a period of one hour and ten minutes. Another batch of'drilling fluid was prepared in the manner given above and the two batches were subsequently mixed.

-This drilling fluid was placed in the hole and drilling proceeded from a depth of 4662 feet to The funnel viscosity (1500/qt.) varied between about 152 to 157 seconds, while the fluid weight remained constant at pounds per cubic foot. --The fluid was un- 7 weighted. The performance of the fluid during the entire drilling was completely satisfactory and the well as completed compared very favorably with those in the immediate vicinity.

The drilling fluids employed in the drilling-of the experimental oil wells described above were A ,the drilling fluid, as herein described, is such'that stable fluids are formed when weightingagents such as insoluble inorganic compounds of the heavy metals including barium sulfate, barium carbonate, ferric oxide or red pigment, plumbic oxide or litharge, galena, silica, pulverized oyster shells, or other similar'materials are used. By

incorporation of these agents in the oil-base drilling fluid described above, fluid weights considerably greater than 60pounds per cubic foot' may be formed.

Somemodiflcationmay be made in-the selec tion of the so-calle'd-heavy oil, the light domestic fuel oil of Example I. The important considera-*- 'tion in heavy oil selection is that it must contain high molecular weight oleflnic or aromatic hydrocarbons, or both, and must be relatively free from normally solid hydrocarbon or hydrocarbon like materials such as asphalt. It may contain considerable quantities of sulfur. These high molecular weight olefinic or aromatic materials serve as suitable wall-forming or wall-sealing agents in the hole only when they are properly dispersed or combined with a light oil having certain characteristics. This has been demonstrated by A. :P. 1., code 29, filtration and viscosity tests. Asalternatesfor. cracked fuel .oil, such materials 17 as straight run fuel oil or road oil, or the like, which fulfill the requirements given above for the heavy oil may be used.

As indicated above, the purpose of the light oil or modifying oil, the gas oil or Diesel fuel of the above examples, depends upon the source and the nature of the heavy oil employed. For example, if a very heavy liquid hydrocarbon is employed a relatively aromatic light oil is desirable. Relatively aromatic light oils are characterized by high aniline point, high VGC or low viscosity index. If a less high molecular weight heavy oil is employed, a light oil which is less aromatic and having a lower aniline point, a lower VGC or higher V. I. should be employed. The important consideration is that the wall sealing properties of the drilling fluid may be controlled by the proper selection of light oil and heavy oil combination.

The soaps employed in the formation of the emulsion present in the improved drilling fluids of this invention are of considerable importance. The cationic constituents of the soaps employed may be selected from the group consisting of the alkali metals and ammonium for the water-dispersible soaps and such other divalent or polyvalent cationic constituents as barium, aluminum, lead, zinc, strontium, magnesium, and the like, may be added as basically reacting compounds such as oxides, hydrated oxides, or hydroxide to metathesize a portion of the waterdispersible soap for the formation of the oildispersible soap. The use of calcium as the cationic constituent is preferred. The preferred anions comprise the rosin acids, while other com stituents such as the naphthenic, fatty carboxylic, and sulfonic acids may be used, the results obtained are not as satisfactory and are listed above in decreasing order of effectiveness as emulsifying and filter loss rate reducing agents.

Although it is preferred to form the oil-dispersible soap in situ by adding excess basic materials such as barium oxide, calcium oxide, lead oxide, zinc oxide, etc., the oil-dispersible soaps may be prepared separately and added during the preparation of the drilling fluid with substantially the same desirable results.

A particular embodiment of the present invention has been hereinabove described in considerable detail by way of illustration. It should be understood that various other modifications and adaptations thereof may be made by those skilled in this particular art without departing from the spirit and scope of this invention as set forth in the appended claims.

I claim:

1. A method for preparing a drilling fluid composition for drilling oil and gas wells which comprises dispersing between about 1.0 and about 1.5 parts by weight of an alkaline-earth metal base in about parts of crude petroleum, adding from about 0.1 to about parts by weight of a water dispersible alkali-metal soap, adding from about 0.05 to about 5 parts by weight of a hydratable clay and from about 0.05 to about 10 parts by weight of water, and thereafter adding sufiicient crude petroleum to make 100 parts by Weight.

2. The method of claim 1 wherein the alkalineearth metal base is hydrated lime and the soap is an alkali-metal rosin soap.

3. A method for preparing a drilling fluid com- 18 position for drilling oil and gas wells which comprises dispersing between about 1.0 and about 1.5 parts by weight of an alkaline-earth metal base in from about 1 to about 20 parts by weight of a light oil boiling between about 300 and about 760 F., adding from about 0.1 to about 10 parts by weight of a water-dispersible alkali-metal soap, adding from about 0.05 to about 5 parts by weight of a hydratable clay and from about 0.05 to about 10 parts by weight of water, and thereafter adding sufificient of a heavy oil having a gravity of between about and 250 API to make 100 parts by weight.

4. The method of claim 3 wherein the alkalineearth metal base is hydrated lime and the soap is an alkali-metal rosin soap.

5. A drilling fluid composition for drilling oil and gas wells prepared by dispersing between about 0.1 and about 10 parts by weight of a water-dispersible alkali-metal soap, between about 1.0 and about 1.5 parts by weight of an alkaline-earth metal base, between about 0.05 and about 5 parts by weight of a hydratable cla Y and between about 0.05 and about 10 parts by weight of water in sufficient mineral oil to make 100 parts by weight.

6. A drilling fluid as defined by claim 5 in which the mineral oil is crude petroleum.

7. A drilling fluid as defined by claim 5 in which the alkaline-earth metal base is selected from the class consisting of calcium oxide and calcium hydroxide.

8. A drilling fluid as defined by claim 5 in which the water-dispersible alkali-metal soap is a water-dispersible alkali-metal soap of an unsaturated cyclic organic acid.

9. A drilling fluid as defined by claim 5 in which the water-dispersible alkali-metal soap is a water-dispersible alkali-metal rosin acid soap.

10. A drilling fluid as defined by claim 5 in which the water-dispersible alkali-metal soap is a Water-dispersible alkali-metal rosin acid soap, the alkaline-earth metal base is hydrated lime, and the mineral oil is crude petroleum.

PAUL W. FISCHER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,099,825 Rolshausen et a1. Nov. 23, 1937 2,214,634 Dombrow Sept. 10, 1940 2,216,955 Moore Oct. 8, 1940 2,297,660 Mozee Sept. 29, 1942 2,350,154 Dawson et al May 30, 1944 2,360,992 Weiss Oct. 24, 1944 2,380,156 Dobson et a1. July 10, 1945 2,423,144 Gregg July 1, 1947 2,430,039 Anderson Nov. 4, 1947 OTHER REFERENCES Alexander: Oil Base Fluids Often Boost Production, article in The Oil Weekly, September 4, 1944, pages 36, 38, and 40.

Miller: Oil Base Drilling Fluids, article in The Petroleum Engineer, Reference Annual, 1947. Pages 84, 88, 90, 93, 94, 96, and 98. 

5. A DRILLING FLUID COMPOSITION FOR DRILLING OIL AND GAS WELLS PREPARED BY DISPERSING BETWEEN ABOUT 0.1 AND ABOUT 10 PARTS BY WEIGHT OF A WATER-DISPERSIBLE ALKALI-METAL SOAP, BETWEEN ABOUT 1.0 AND ABOUT 1.5 PARTS BY WEIGHT OF AN ALKALINE-EARTH METAL BASE, BETWEEN ABOUT 0.05 AND ABOUT 5 PARTS BY WEIGHT OF A HYDRATABLE CLAY AND BETWEEN ABOUT 0.05 AND ABOUT 10 PARTS BY WEIGHT OF WATER IN SUFFICIENT MINERAL OIL TO MAKE 100 PARTS BY WEIGHT. 